coverage of system initialization unique to a BusyBox environment. Appendix C, 'BusyBox Commands,' lists the available BusyBox commands from a recent BusyBox release.
Chapter 12, 'Embedded Development Environment,' takes a detailed look at the unique requirements of a typical cross-development environment. Several techniques are presented to enhance your productivity as an embedded developer, including the powerful NFS root mount development configuration.
Chapter 13, 'Development Tools,' examines many useful development tools. Debugging with gdb is introduced, including coverage of core dump analysis. Many more tools are presented and explained, with examples including strace, ltrace, top, and ps, and the memory profilers mtrace and dmalloc. The chapter concludes with an introduction to the more important binary utilities, including the powerful readelf utility.
Chapter 14, 'Kernel Debugging Techniques,' provides a detailed examination of many debugging techniques useful for debugging inside the Linux kernel. We introduce the use of the kernel debugger KGDB, and present many useful debugging techniques using the combination of gdb and KGDB as debugging tools. Included is an introduction to using hardware JTAG debuggers and some tips for analyzing failures when the kernel won't boot.
Chapter 15, 'Debugging Embedded Linux Applications,' moves the debugging context from the kernel to your application programs. We continue to build on the gdb examples from the previous two chapters, and we present techniques for multithreaded and multiprocess debugging.
Chapter 16, 'Porting Linux,' introduces the issues related to porting Linux to your custom board. We walk through a simple example and highlight the steps taken to produce a working Linux kernel on a custom PowerPC board. Several important concepts are presented that have trapped many newcomers to Linux kernel porting. Together with the techniques presented in Chapters 13 and 14, you should be ready to tackle your own custom board port after reading this chapter.
Chapter 17, 'Linux and Real Time,' provides an introduction to one of the more exciting developments in embedded Linux: configuring for real time via the CONFIG_RT option. We cover the features available with RT and how they can be used in a design. We also present techniques for measuring latency in your application configuration.
The appendixes cover the GNU Public License, U-Boot Configurable Commands, BusyBox Commands, SDRAM Interface Considerations, resources for the open source developer, and a sample configuration file for one of the more popular hardware JTAG debuggers, the BDI-2000.
Follow Along
You will benefit most from this book if you can divide your time between the pages of this book and your favorite Linux workstation. Grab an old x86 computer to experiment on an embedded system. Even better, if you have access to a single-board computer based on another architecture, use that. You will benefit from learning the layout and organization of a very large code base (the Linux kernel), and you will gain significant knowledge and experience as you poke around the kernel and learn by doing.
Look at the code and try to understand the examples produced in this book. Experiment with different settings, configuration options, and hardware devices. Much can be gained in terms of knowledge, and besides, it's loads of fun!
GPL Copyright Notice
Portions of open-source code reproduced in this book are copyrighted by a large number of individual and corporate contributors. The code reproduced here has been licensed under the terms of the GNU Public License or GPL.
Appendix A contains the text of the GNU General Public License.
Acknowledgments
I am constantly amazed by the graciousness of open source developers. I am humbled by the talent in our community that often far exceeds my own. During the course of this project, I reached out to many people in the Linux and open source community with questions. Most often my questions were quickly answered and with encouragement. In no particular order, I'd like to express my gratitude to the following members of the Linux and open source community who have contributed answers to my questions:
Dan Malek provided inspiriation for some of the contents of Chapter 2, 'Your First Embedded Experience.'
Dan Kegel and Daniel Jacobowitz patiently answered my toolchain questions.
Scott Anderson provided the original ideas for the gdb macros presented in Chapter 14, 'Kernel Debugging Techniques.'
Brad Dixon continues to challenge and expand my technical vision through his own.
George Davis answered my ARM questions.
Jim Lewis provided comments and suggestions on the MTD coverage.
Cal Erickson answered my gdb use questions.
John Twomey advised on Chapter 3, 'Processor Basics.'
Lee Revell, Sven-Thorsten Dietrich, and Daniel Walker advised on real time Linux content.
Many thanks to AMCC, Embedded Planet, Ultimate Solutions, and United Electronic Industries for providing hardware for the examples. Many thanks to my employer, Monta Vista Software, for tolerating the occasional distraction and for providing software for some of the examples. Many others contributed ideas, encouragement, and support over the course of the project. To them I am also grateful.
I wish to acknowledge my sincere appreciation to my primary review team, who promptly read each chapter and provided excellent feedback, comments, and ideas. Thank you Arnold Robbins, Sandy Terrace, Kurt Lloyd, and Rob Farber. Many thanks to Arnold for helping this newbie learn the ropes of writing a technical book. While every attempt has been made to eliminate mistakes, those that remain are solely my own.
I want to thank Mark L. Taub for bringing this project to fruition and for his encouragement and infinite patience! I wish to thank the production team including Kristy Hart, Jennifer Cramer, Krista Hansing, and Cheryl Lenser.
And finally, a very special and heartfelt thank you to Cary Dillman who read each chapter as it was written, and for her constant encouragement and her occasional sacrifice throughout the project.
Chris Hallinan
About the Author
Christopher Hallinan is currently field applications engineer for Monta Vista Software, living and working in Massachusetts. Chris has spent more than 25 years in the networking and communications marketplace mostly in various product development roles, where he developed a strong background in the space where hardware meets software. Prior to joining Monta Vista, Chris spent four years as an independent Linux consultant providing custom Linux board ports, device drivers, and bootloaders. Chris's introduction to the open source community was through contributions to the popular U-Boot bootloader. When not messing about with Linux, he is often found singing and playing a Taylor or Martin.
